The proposal continues our previous research on the biological and psychological mechanisms of communication and social behavior in marmosets and tamarins. These monkeys have a highly developed vocal communication system and a social system with monogamous breeding and a nuclear family. Both of these have interesting parallels in human behavior. Our previous studies demonstrated parallels between vocalizations and aspects of speech and language. Techniques were developed to separate linguistic and paralinguistic components of signals; subtle variations in phonetic structure was correlated with specific situations; monkeys were shown to perceive their calls categorically as we perceive speech; and a rudimentary grammar was demonstrated. Future work will examine semantic and syntactic structures by measuring responses of monkeys to normal and abnormal structures. Further studies in categorical perception will be completed. Ontogeny of vocal communication will be thoroughly studied to see if learning is involved. All of these studies are aimed at developing an animal model for studying human speech and language disorders. Breeding biology will also be studied by the measurement of urinary gonadal steroids to determine normal ovulatory cycles in females and to determine the mechanisms by which daughters are kept from breeding within their family group. Monogamous animals typically show extensive parental care by fathers older siblings. Adequate parental care must be learned in these species, and our research will attempt to determine the important components of the achievement of parental competence. Most primates which are studied are either polygynous or promiscuous and hence do not provide good models for human social behavior. Finally, we will study the cognitive abilities of these monkeys to learn what their intellectual capacities are and how they perceptually organize their world.